The present invention relates to a technology for improving reliability of a storage device. More specifically, the present invention relates to a technology effectively applied to data saving in a storage device comprising nonvolatile semiconductor memory.
Memory cards have rapidly spread as a storage device for personal computers and multifunctional terminals. With increasing demands for high performance in recent years, for example, flash memory is used as semiconductor memory installed in a memory card. The flash memory is capable of electrically erasing and rewriting data and storing a large amount of data without using a battery.
When the semiconductor memory malfunctions, some memory cards allow the faulty semiconductor memory to be replaced by an alternative semiconductor memory for preventing the memory card from being unusable (e.g., see patent document 1).
[Patent document 1]
Japanese Unexamined Patent Publication No. Hei 3(1991)-191450